Cops showed up at R. Kelly’s birthday celebration at a Chicago nightclub … responding to a call about a warrant for the singer’s arrest.

TMZ reports that Kelly was partying at V75 Nightclub early Thursday morning when cops say someone tipped them off … calling them to say Kelly was there, and had a warrant for his arrest.

Law enforcement confirmed that they did indeed go to the club and make contact with Kelly — however, once they determined there was no actual arrest warrant … Kelly was free to go about his business.

It’s unclear if the caller was just pranking Kelly, or if the person really thought there was an arrest warrant … but cops insist they routinely respond to such calls … just to make sure.

As for Kelly’s party … he was surrounded by screaming fans as he grabbed the mic and announced he was gonna party for his birthday regardless of the controversy swirling around him after the airing of Surviving R. Kelly.

Strange as it sounds … Kelly had tons of fans on hand gassing him up as he sang the opening to Bump N’ Grind.